1. Field of the Invention
The present invention relates to a spin-valve type magnetoresistive head with the electric resistance changeable by the relationship between the magnetization direction of a pinned magnetic layer and the magnetization direction of a free magnetic layer affected by the external magnetic field, in particular, to a spin-valve type magnetoresistive element capable of appropriately controlling the magnetization of a free magnetic layer without the need of providing a hard bias layer.
2. Description of the Related Art
FIG. 3 is a cross-sectional view showing a conventional configuration of a spin-valve type magnetoresistive element or a spin-valve type magnetoresistive head for detecting a recording magnetic field from a recording medium such as a hard disk.
As shown in the figure, an antiferromagnetic layer 1, a pinned magnetic layer 2, a non-magnetic electrically conductive layer 3, and a free magnetic layer 4 are formed, with hard bias layers 5, 5, provided at both ends thereof.
Conventionally, in general, the antiferromagnetic layer 1 comprises an Fe--Mn (iron-manganese) alloy film or an Ni--Mn (nickel-manganese) alloy film. The pinned magnetic layer 2 and the free magnetic layer 4 comprise an Fe--Ni (iron-nickel) alloy film. The non-magnetic electrically conductive layer 3 comprises a Cu (copper) film. The hard bias layers 5, 5, comprise a Co--Pt (cobalt-platinum) alloy film. Numerals 6, 7 represent a base layer and a protection layer made from a non-magnetic material such as Ta (tantalum).
As shown in the figure, the antiferromagnetic layer 1 and the pinned magnetic layer 2 are formed adjacent to each other. The pinned magnetic layer 2 is in a single domain state in the Y direction by the exchange anisotropic magnetic field by the exchange coupling at the interface with the antiferromagnetic layer 1 so that the magnetization direction is fixed to the Y direction. The exchange anisotropic magnetic field is generated at the interface between the antiferromagnetic layer 1 and the pinned magnetic layer 2 by applying an annealing treatment (thermal treatment) while applying a magnetic field in the Y direction.
By the influence from the hard bias layers 5, 5, magnetized in the X direction, the magnetization direction of the free magnetic layer 4 is aligned in the X direction.
An antiferromagnetic material has the inherent blocking temperature. By exceeding the temperature, the exchange anisotropic magnetic field at the interface between the antiferromagnetic layer and the magnetic layer is vanished.
Therefore, the annealing treatment for putting the pinned magnetic layer 2 in a single domain state by the exchange anisotropic magnetic field at the interface between the antiferromagnetic layer 1 and the pinned magnetic layer 2 needs to be conducted at a temperature lower than the blocking temperature of the antiferromagnetic material comprising the antiferromagnetic layer 1. If a thermal treatment is applied at the blocking temperature or higher, the exchange anisotropic magnetic field is weakened (or vanished) so that the pinned magnetic layer 2 cannot be put in a single domain state in the Y direction to generate a problem of a large noise of the detection output.
The blocking temperature of an Fe--Mn alloy film conventionally used as the antiferromagnetic layer 1 is about 150.degree. C., and the blocking temperature of an Ni--Mn alloy film is about 400.degree. C.
The spin-valve type magnetoresistive element shown in FIG. 3 can be produced by forming 6 layers from the lower layer 6 to the protection layer 7, abrading out the side part of the 6 layers by an etching process such as an ion milling so as to have an inclined surface with an angle .theta., and forming the hard bias layers 5, 5 at both ends of the 6 layers.
In the spin-valve type magnetoresistive element, a stationary current (detection current) is provided from electrically conductive layers 8, 8 formed on the hard bias layers 5, 5 to the pinned magnetic layer 2, the non-magnetic electrically conductive layer 3, and the free magnetic layer 4. The running direction of a recording medium such as a hard disk is the Z direction. If the current is provided in the direction of the leakage magnetic field Y from the recording medium, the magnetization of the free magnetic layer 4 changes from the X direction to the Y direction. The electric resistance is changed by the relationship between the change of the magnetization direction in the free magnetic layer 4 and the pinned magnetization direction in the pinned magnetic layer 2. The leakage magnetic field from the recording medium can be detected by the voltage change based on the electric resistance value change.
Since the spin-valve type magnetoresistive element shown in FIG. 2 has the hard bias layers 5, 5, at both sides of the 6 layers from the base layer 6 to the protection layer 7, the below-mentioned problems are involved.
The angle .theta. of the inclined surface formed in the side part of the 6 layers from the base layer 6 to the protection layer 7 should be in an optional range. If the inclined surface is formed with an angle .theta. outside the range, the leakage magnetic field from the hard bias layers 5, 5 in the X direction cannot be transmitted to the free magnetic layer 4 well so that it involves a problem in that the magnetization direction of the free magnetic layer 4 cannot be aligned completely in the X direction. Unless the magnetization direction of the free magnetic layer 4 is completely aligned in a single magnetic domain in the X direction, reproduction characteristics are affected such as generation of a Barkhausen noise.
Furthermore, in the spin-valve type magnetoresistive element shown in FIG. 3, the hard bias layers 5, 5 formed at both sides of the free magnetic layer 4 has a thin film thickness so that a sufficient bias magnetic field cannot be applied to the free magnetic layer 4 in the X direction. Therefore, it is disadvantageous in that the magnetization direction of the free magnetic layer 4 cannot be stable in the X direction, and thus a Barkhausen noise can be easily generated.
Moreover, the hard bias layers 5, 5 formed at both sides of the pinned magnetic layer 2 have a comparatively thick film thickness so that the pinned magnetic layer 2 receives a comparatively strong bias magnetic field from the hard bias layers 5, 5 in the X direction.
As heretofore mentioned, the magnetization of the pinned magnetic field 2 is fixed in the Y direction by the exchange anisotropic magnetic field at the interface with the antiferromagnetic layer 1, however, it may involve a problem in that the magnetization can be affected to change by the bias magnetic field from the hard bias layers 5, 5 in the X direction so that the leakage magnetic field from the recording medium cannot be detected well unless the magnetization of the pinned magnetic layer 2 is fixed firmly in the Y direction.